What Is Auditory Grouping by Frequency Similarity?

By its very nature, sound unfolds in time, so it’s important to understand the principles that the auditory system uses to group frequencies that occur at different times—that is, sequentially rather than simultaneously. Sequences of pure tones provide a simple context for revealing these principles.


Figure 1

Figure 1 illustrates how the auditory system uses the frequency similarity of sequential tones to group those tones into a single auditory stream or into two separate auditory streams. When a listener hears a sequence of pure tones that vary between two frequencies, and the alternating frequencies are close to one another, then the listener often perceives the sequence as a single auditory stream, warbling up and down. This is shown in the top panel of the figure, where the frequencies of tone A and tone B are close and the sequence A B A A B A . . . is perceived as a single stream. In contrast, as shown in the bottom panel, if the two alternating tones are far apart in frequency, then the listener perceives two separate auditory streams, a lower-frequency sequence A A A . . . and a higher-frequency sequence C C C . . . .

Auditory Grouping by Frequency Similarity

Explore how your auditory system groups tones of different frequencies into one or more auditory streams.

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When a bird sings, it tends to emit notes of similar frequencies. If you suddenly heard a note with a very different frequency, you might think that another bird had started singing.
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In this demonstration, you'll explore how your auditory system uses differences in frequency to group a sequence of tones into one or more auditory streams. When you click PLAY, you'll hear two tones, A and B, in the repeated sequence ABA ABA ABA ...

 

You can vary the frequency of Tone B by dragging the slider up and down the Frequency axis. The frequency of Tone A is fixed at an intermediate level.

 

Can you determine how your perception of one versus two auditory streams depends on the difference in frequency between Tone A and Tone B?

Tone B
Frequency

Tone A

Time
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What Is Auditory Grouping by Frequency Similarity?

By its very nature, sound unfolds in time, so it’s important to understand the principles that the auditory system uses to group frequencies that occur at different times—that is, sequentially rather than simultaneously. Sequences of pure tones provide a simple context for revealing these principles.

Figure 1 illustrates how the auditory system uses the frequency similarity of sequential tones to group those tones into a single auditory stream or into two separate auditory streams. When a listener hears a sequence of pure tones that vary between two frequencies, and the alternating frequencies are close to one another, then the listener often perceives the sequence as a single auditory stream, warbling up and down. This is shown in the top panel of the figure, where the frequencies of tone A and tone B are close and the sequence A B A A B A . . . is perceived as a single stream. In contrast, as shown in the bottom panel, if the two alternating tones are far apart in frequency, then the listener perceives two separate auditory streams, a lower-frequency sequence A A A . . . and a higher-frequency sequence C C C . . . .


Figure 1

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Select your answer to the question below. Then click SUBMIT.

Why is it important to understand the principles that the auditory system uses to group sequences of pure tones of different frequencies?

A. Because sound unfolds over time, and sequences of pure tones provide a simple example of this.
B. Because most sounds consist of sequences of pure tones.
C. Because sequences of pure tones of different frequencies are always grouped into a single auditory stream.
D. Because sequences of pure tones of different frequencies are never grouped into a single auditory stream.
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Select your answer to the question below. Then click SUBMIT.

Tone A and Tone B are close in frequency. How would a listener be likely to group the sequence BAB BAB BAB…?

A. As two distinct auditory streams.
B. As a single auditory stream.
C. No grouping is likely.
D. Grouping is likely to alternate between two distinct auditory streams and a single auditory stream.
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Select your answer to the question below. Then click SUBMIT.

Tone A and Tone B are far apart in frequency. How would a listener be likely to group the sequence ABA ABA ABA…?

A. As two distinct auditory streams.
B. As a single auditory stream.
C. No grouping is likely.
D. Grouping is likely to alternate between two distinct auditory streams and a single auditory stream.
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Auditory Grouping by Frequency Similarity.

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